The error may have been to hold on to the broken kindle before receiving the replacement. When my kindles failed, I returned them immediately when I recieved the email with the label attached.

It takes time for Amazon to receive the returned kindle. If its held too long or takes too long in delivery, Amazon may automatically close the account. They can check the UPS or USPS label number and see if the customer returned it. If they cannot track the customer return, the customer account may be automatically closed permanently.

Also, insulting or defensive statements made to Amazon Customer Support may also result in a closed account. Finally, if one has a merchandise dispute with Amazon and has one's bank do a charge back to Amazon, that could also end one's account.